The synthesis, structure and photoluminescent properties of solid-state green to yellow emitters based on β-carboline

Article abstract of DOI:10.1016/j.dyepig.2012.06.002

A series of solid-state green to yellow emitters based on β-carboline core were synthesized and characterized. The crystal structures of four of them were determined by single crystal X-ray diffraction analysis. The photoluminescent properties of β-carbol

Full text of DOI:10.1016/j.dyepig.2012.06.002

Dyes and Pigments 95 (2012) 512e522
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis, structure and photoluminescent properties of solid-state green
to yellow emitters based on
b-carboline
,
b
,
a
a
a
b
a
Yi-Feng Sun a , Zhi-Yong Chen , Ya-Ling Liu , Na Li , Ji-Kun Li , Hua-Can Song
*
a Guangdong Provincial Public Laboratory of Analysis and Testing Technology, China National Analytical Center, Guangzhou 510070, PR China
b School of Chemistry and Chemical Engineering, Taishan University, Taian 271021, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of solid-state green to yellow emitters based on b-carboline core were synthesized and char-
Received 10 May 2012
Received in revised form
2 June 2012
Accepted 5 June 2012
Available online 12 June 2012
acterized. The crystal structures of four of them were determined by single crystal X-ray diffraction
analysis. The photoluminescent properties of -carbolines were examined in solution and in the solid
b
state. It was found that these fluorophores were luminescent, having solid-state emission at wavelengths
ranging from 505 to 582 nm, depending on structure. Significantly, two naphthalene-carboline hybrids
exhibit strong green fluorescence emission both in solution and in crystalline state. However,
two methoxyl-phenyl substituted b-carboline derivative show intense green/yellow emission peaked at
Keywords:
540e582 nm, and display red-shifted by 40e82 nm with respect to the solution behavior. The experi-
mental results demonstrated that the solid-state emission ranging from green to yellow can be readily
tuned by simply varying molecular structure. The solid-state luminescent properties are highly depen-
dent on the nature and position of the substituents and also on the molecular arrangements and the
intermolecular interactions.
b-Carboline
Acylhydrazone
Synthesis
Crystal structure
Emission enhancement
Photoluminescence
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
preferentially the s-cis conformation of 3-carboxy-b-carbolines or
one approaching this geometry [13].
The
b
-carboline unit, a tricyclic nitrogen-containing pharma-
Apart from their pharmacological properties, this class of
compounds is good fluorophores [14], and has also been used as
photosensitizers with potential application in photodynamic
therapy [15], and as fluorescent standards [16e18] or as indicators
cophore constituted by the fusion of an indole ring and a pyridine
ring, can be found in a great many bioactive compounds of both
natural and synthetic origin.
b-Carboline derivatives have long
been recognized to possess an extremely wide span of interesting
biological activities [1e3], especially the central nervous system
(CNS) and antitumor properties. Therefore, great efforts have been
for small acidities in the physiological pH range [14]. Besides, b-
carbolines have also been reported to be capable of experiencing
phototautomerism [19].
devoted to the synthesis and biological evaluation of various new
carboline alkaloids [4e10]. Furthermore, studies on
structureeactivity relationship have demonstrated the influence of
the position and nature of ring-substituents on the activity of
carboline derivatives. For example, the introduction of appro-
priated substituents into position-1, -2, -3 and -9 of the -carboline
b
-
In fact, much recent attention has been focused mainly on the
synthesis, characterization and biological evaluation of b-carboline
derivatives, whereas less explored are their structure and photo-
physical properties, although some cases have been described in
b
-
the literature [20e24]. In particular, only a few simple
are employed in these studies, such as norharman, harman, har-
mine and methyl -carboline-3-carboxylate ( CCM) (Fig. 1). To the
best of our knowledge, however, unlike the carbazole analogs,
b-carbolines
b
skeleton resulted in more potent antitumor derivatives, with
decreasing acute toxicity [11,12]. Moreover, previous research has
b
b
b
-
suggested that substitution at the position-3 of a
an ester function was necessary for the high affinity binding to the
b
-carboline with
carbolines have never been investigated previously for their solid-
state luminescent properties.
central benzodiazepine receptors (BZR), and the BZR recognized
In view of the emission properties and potential applications of
these compounds, and the continued interest in the development
of solid-state organic luminescent materials, the focus of the
current research workers turned toward the synthesis, crystallog-
* Corresponding author. School of Chemistry and Chemical Engineering, Taishan
University, Taian 271021, PR China. Tel.: þ86 20 37656300; fax: þ86 20 87686511.
E-mail address: sunyf50@yahoo.com.cn (Y.-F. Sun).
raphy and optical evaluation of novel
b-carboline derivatives. The
solid-state photoluminescent properties of novel
b-carbolines are
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.06.002

Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
513
COOCH
3
N
N
N
N
N
H
N
H
H CO
3
N
H
N
H
CH
CH
3
3
Methyl β-carboline-3-carboxylate (βCCM)
CCM.
Norharman
Harman
Harmine
Fig. 1. The structures of Norharman, Harman, Harmine and
b
discussed. The structures were investigated to obtain insights on
the possible origins of solid-state luminescent properties. The
synthetic pathway and the structures of target molecules are
shown in Figs. 2 and 3.
J ¼ 0.6 Hz, 1H), 9.74 (s, 1H). 13C NMR (75 MHz, DMSO-d6/TMS)
d:
46.08, 110.74, 113.75, 120.40, 120.86, 122.49, 126.84, 127.53, 128.02,
128.69, 128.87, 131.45, 137.17, 139.92, 141.27, 163.80. Anal. calcd for
C19H16N4O: C 72.14, H 5.10, N 17.71; found: C 72.21, H 5.19, N 17.62.
2.3. Synthesis of N0-arylidene-
b-carboline-3-carbohydrazides (4)
2. Experimental
2.1. General
A mixture of -carboline-3-carbohydrazides 3 (2 mmol) and the
b
appropriate aryl aldehydes (2 mmol) in anhydrous ethanol (30 mL)
was heated under reflux for 6 h. After cooling, the solid was filtrated
and recrystallized from ethanole N,N0-dimethylformamide (DMF)
to afford the pure product.
1H NMR and 13C NMR spectra were taken on a Bruker AVANCE-
300 NMR spectrometer and chemical shifts expressed as
d (ppm)
values with TMS as internal standard. Element analysis was taken
with a PerkineElmer 240 analyzer. Mass spectra (MS) were
measured on an Agilent LC/MSD Trap XCT mass spectrometer with
an electrospray ionization source in positive ion mode. Absorption
spectra were determined on a Hitachi U-3900 UVeVis scanning
spectrophotometer. The solution phase photoluminescence spectra
were determined with a Hitachi F-2500 spectrometer and the slit
widths were 5 nm for both excitation and emission. The solid-state
photoluminescence spectra were measured using a Horiba Jobin-
Yvon LabRam HR UV-NIR Confocal Laser MicroRaman spectrom-
eter under a 325 nm HeeCd laser excitation. Single crystal was
characterized by Bruker Smart 1000 CCD X-ray single-crystal
diffractometer. The melting points were determined with a WRS-
1A melting point apparatus and are uncorrected. All reagents and
chemicals are commercially available and used without further
purification. The starting compounds 2 were prepared according to
reported methods [11,25,26].
2.3.1. N0-(2-hydroxyl-1-naphthylmethylene) -
b-carboline-3-
carbohydrazide (4a)
Yellow crystals, yield 69%; mp ＞250 ꢀC；1H NMR (300 MHz,
DMSO-d6/TMS)
d
: 7.26 (d, J ¼ 9.0 Hz, 1H), 7.34 (t, J ¼ 7.8 Hz, 1H), 7.42
(t, J ¼ 7.2 Hz, 1H), 7.61 (d, J ¼ 6.9 Hz, 1H), 7.66 (d, J ¼ 8.1 Hz, 1H), 7.71
(d, J ¼ 8.1 Hz,1H), 7.93 (t, J ¼ 9.3 Hz, 2H), 8.23 (d, J ¼ 8.4 Hz,1H), 8.47
(d, J ¼ 7.8 Hz, 1H), 9.02 (d, J ¼ 0.9 Hz, 1H), 9.03 (s, 1H), 9.87 (s, 1H),
12.09 (s, 1H), 12.56 (s, 1H), 13.16 (s, 1H). 13C NMR (75 MHz, DMSO-
d6/TMS) d: 108.65, 112.36, 115.26, 118.97, 120.21, 120.47, 120.88,
122.39, 123.48, 127.63, 127.75, 128.26, 128.82, 128.92, 131.81, 132.50,
137.26, 141.03, 157.96, 160.90. ESI-MS m/z: 381.4 (M þ H)þ. Anal.
calcd for C23H16N4O2: C 72.62, H 4.24, N 14.73; found: C 72.54, H
4.29, N 14.65.
2.3.2. N0-(2,4-dihydroxybenzlidene) -
b-carboline-3-carbohydrazide
(4b)
2.2. Synthesis of
b-carboline-3-carbohydrazides (3)
Off-white solid, yield 58%; mp ＞250 ꢀC；1H NMR (300 MHz,
DMSO-d6/TMS)
d
: 6.34 (d, J ¼ 2.1 Hz, 1H), 6.38 (dd, J ¼ 8.1, 2.1 Hz,
2.2.1. -Carboline-3-carbohydrazide (3a)
b
1H), 7.23 (d, J ¼ 8.4 Hz, 1H), 7.31 (t, J ¼ 8.1 Hz, 1H), 7.61 (t, J ¼ 8.1 Hz,
1H), 7.69 (d, J ¼ 8.4 Hz, 1H), 8.44 (d, J ¼ 8.1 Hz, 1H), 8.73 (s, 1H), 8.96
(s, 2H), 9.99 (s, 1H), 11.82 (s, 1H), 12.04 (s, 1H), 12.27 (s, 1H). 13C NMR
80% hydrazine hydrate (20 mL) was added to the suspension of
2a (8 mmol) in ethanol (80 mL), the mixture was refluxed for 7 h.
After cooling, the precipitate was collected by filtration, washed
with ethanol, and then dried. The crude product was recrystallized
from ethanol to give 3a as silver plates, yield 71%, mp ＞250 ꢀC (Lit.
mp 289e291 ꢀC [27]).
(75 MHz, DMSO-d6/TMS) d: 102.70, 107.60, 110.62, 112.31, 115.01,
120.13, 120.87, 122.34, 128.21, 128.75, 131.62, 132.38, 137.34, 138.61,
141.00, 149.83, 159.61, 160.54, 160.86. ESI-MS m/z: 347.3 (M þ H)þ.
Anal. calcd for C19H14N4O3: C 65.89, H 4.07, N 16.18; found: C 65.81,
H 4.02, N 13.91.
2.2.2. 9-Benzyl-b-carboline-3-carbohydrazide (3b)
This compound was prepared from 2b and hydrazine hydrate
according to the procedure described for 3a. Colorless crystals,
yield 68%; mp 207e209 ꢀC (Lit. 209e211 ꢀC [28])； 1H NMR
2.3.3. N0-(2-hydroxy-3-methoxybenzlidene) -
b-carboline-3-
carbohydrazide (4c)
Pale yellow solid, yield 60%; mp ＞250 ꢀC；1H NMR (300 MHz,
(300 MHz, DMSO-d6/TMS)
d
: 4.59 (s, 2H), 5.86 (s, 2H), 7.22e7.32 (m,
DMSO-d6/TMS)
d
: 3.85 (s, 3H), 6.90 (t, J ¼ 7.8 Hz, 1H), 7.07 (t,
5H), 7.35 (t, J ¼ 7.8 Hz, 1H), 7.65 (t, J ¼ 8.1 Hz, 1H), 7.81 (d, J ¼ 8.4 Hz,
J ¼ 8.8 Hz, 2H), 7.34 (t, J ¼ 7.5 Hz, 1H), 7.64e7.73 (m, 2H), 8.47 (d,
1H), 8.47 (d, J ¼ 7.8 Hz, 1H), 8.87 (d, J ¼ 0.6 Hz, 1H), 9.08 (d,
J ¼ 7.8 Hz, 1H), 8.88 (s, 1H), 9.00 (s, 1H), 9.02 (s, 1H), 11.49 (s, 1H),
O
COOH
COOC H
CONHNH
2
2
5
i , ii , iii
N
Ar
v
N
H
NH
2
vi
N
N
H
N
N
R
N
R
N
N
R
1
2a
R = H
2b R = CH C H
6 5
3a
R = H
3b R = CH C H
6 5
4a - 4g
iv
2
2
Fig. 2. Synthesis of the
b-carboline-based fluorophores. Reagents and reaction conditions: (i) HCHO, NaOH; (ii) EtOH, HCl; (iii) S, Xylene, reflux; (iv) Benzyl bromide, DMF, NaH,
reflux; (v) NH2NH2$H2O, EtOH, reflux; (vi) Aryl aldehyde, EtOH, Glacial acetic acid, reflux.

514
Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
OCH
3
HO
HO
OH
HO
O
O
O
N
N
N
N
H
N
H
N
H
N
N
N
N
H
N
H
N
H
4a
4b
4c
OH
OCH
3
HO
HO
OH
HO
HO
O
O
O
O
N
N
N
N
N
H
N
H
N
H
N
H
N
N
N
N
N
N
N
N
4d
4e
4f
4g
Fig. 3. The structures of the b-carboline-based fluorophores.
12.09 (s, 1H), 12.50 (s, 1H). 13C NMR (75 MHz, DMSO-d6/TMS)
d:
2.3.7. N0-(2-hydroxy-3-methoxybenzlidene)-9-benzyl-
b-carboline-
55.78, 112.32, 113.75, 115.25, 118.79, 118.92, 120.17, 120.87, 121.37,
122.35, 128.22, 128.78, 132.42, 137.42, 138.42, 141.01, 147.34, 147.91,
149.04, 161.21. ESI-MS m/z: 361.2 (M þ H)þ. Anal. calcd for
C20H16N4O3: C 66.66, H 4.48, N 15.55; found: C 66.52, H 4.57, N
15.63.
3-carbohydrazide (4g)
Pale yellow solid, yield 62%; mp 226e228 ꢀC；1H NMR
(300 MHz, DMSO-d6/TMS) d: 3.84 (s, 3H), 5.91 (s, 2H), 6.88 (t,
J ¼ 8.1 Hz, 1H), 7.04e7.11 (m, 2H), 7.24e7.41 (m, 6H), 7.66 (t,
J ¼ 8.4 Hz,1H), 7.83 (d, J ¼ 8.4 Hz,1H), 8.52 (d, J ¼ 7.8 Hz,1H), 8.87 (s,
1H), 9.05 (d, J ¼ 0.9 Hz, 1H), 9.19 (d, J ¼ 0.9 Hz, 1H), 11.44 (s, 1H),
2.3.4. N0-(2-hydroxyl-1-naphthylmethylene)-9-benzyl-
b
-carboline-
12.47 (s, 1H). 13C NMR (75 MHz, DMSO-d6/TMS)
d: 46.21, 55.80,
3-carbohydrazide (4d)
110.87, 113.79, 115.15, 118.81, 118.92, 120.65, 120.86, 121.34, 122.61,
126.87, 127.58, 128.25, 128.73, 129.06, 131.45, 137.06, 137.62, 139.03,
141.36, 147.35, 147.92, 149.08, 161.10. ESI-MS m/z: 451.1 (M þ H)þ.
Anal. calcd for C27H22N4O3: C 71.99, H 4.92, N 12.44; found: C
71.87 H 4.98, N 12.35.
Yellow crystals, yield 66%; mp ＞250 ꢀC；1H NMR (300 MHz,
DMSO-d6/TMS) d: 5.93 (s, 2H), 7.24e7.45 (m, 8H), 7.60e7.70 (m,
2H), 7.82 (d, J ¼ 8.7 Hz, 1H), 7.93 (t, J ¼ 9.4 Hz, 2H), 8.23 (d,
J ¼ 8.7 Hz, 1H), 8.53 (d, J ¼ 7.8 Hz, 1H), 9.08 (d, J ¼ 0.9 Hz, 1H), 9.24
(d, J ¼ 0.9 Hz, 1H), 9.87 (s, 1H), 12.57 (s, 1H), 13.18 (s, 1H). 13C NMR
(75 MHz, DMSO-d6/TMS) d: 46.24, 108.64, 110.89, 115.14, 118.95,
2.4. X-ray crystallography
120.45, 120.66, 120.86, 122.62, 123.47, 126.89, 127.60, 127.74, 128.27,
128.74, 128.91, 129.07, 131.52, 131.81, 132.49, 137.06, 137.69, 138.83,
141.36, 147.43, 157.98, 160.78. ESI-MS m/z: 471.5 (M þ H)þ. Anal.
calcd for C30H22N4O2: C 76.58, H 4.71, N 11.91; found: C 76.51, H
4.80, N 11.83.
X-ray quality crystals of 4b, 4d, 4e and 4f were obtained by slow
evaporation of ethanol-DMF solution. The diffraction data for these
four structures were collected on a Bruker Smart Apex 1000 CCD X-
ray single crystal diffractometer with a graphite monochromated
Mo K
a
radiation (
l
¼ 0.071,073 nm) at 298(2) K. The structures
2.3.5. N0-(2,4-Dihydroxybenzlidene)-9-benzyl-
b-carboline-3-
were solved by direct methods with SHELXS-97 program and
refinements on F2 were performed with SHELXL-97 program by
full-matrix least-squares techniques with anisotropic thermal
parameters for the non-hydrogen atoms. All H atoms were initially
located in a difference Fourier map. The methyl H atoms were then
constrained to an ideal geometry, with CeH ¼ 0.096 nm and
Uiso(H) ¼ 1.5Ueq(C). H atoms bonded to N and O atoms were treated
as riding atoms, with NeH ¼ 0.086 nm, OeH ¼ 0.082e0.085 nm
and Uiso(H) ¼ 1.2Ueq(N) or Uiso(H) ¼ 1.5 Ueq(O). All of the other H
atoms were placed in geometrically idealized positions and con-
strained to ride on their parent atoms, with CeH ¼ 0.093e0.097 nm
and Uiso(H) ¼ 1.2Ueq(C). A summary of the crystallographic data and
structure refinement details is compiled in Table 1.
carbohydrazide (4e)
Pale yellow crystals, yield 62%; mp ＞250 ꢀC；1H NMR
(300 MHz, DMSO-d6/TMS)
d: 5.91 (s, 2H), 6.39e6.44 (m, 2H),
7.23e7.35 (m, 6H), 7.38 (t, J ¼ 7.8 Hz, 1H), 7.65 (t, J ¼ 8.1 Hz,1H), 7.82
(d, J ¼ 8.4 Hz, 1H), 8.52 (d, J ¼ 7.8 Hz, 1H), 8.76 (s, 1H), 9.03 (d,
J ¼ 0.9 Hz, 1H), 9.20 (d, J ¼ 0.6 Hz, 1H), 10.03 (s, 1H), 11.84 (s, 1H),
12.29 (s, 1H). 13C NMR (75 MHz, DMSO-d6/TMS)
d: 46.70, 103.22,
108.13, 111.13, 111.34, 115.42, 121.10, 121.34, 123.08, 127.36, 128.07,
128.75, 129.21, 129.53, 131.90, 132.12, 137.56, 138.05, 139.71, 141.84,
150.41, 160.14, 161.09, 161.26. ESI-MS m/z: 437.3 (M þ H)þ. Anal.
calcd for C26H20N4O3: C 71.55, H 4.62, N 12.84; found: C 71.62, H
4.71, N 12.75.
2.3.6. N0-(2,3-Dihydroxybenzlidene)-9-benzyl-
b-carboline-3-
carbohydrazide (4f)
3. Results and discussion
Yellow crystals, yield 58%; mp 227e229 ꢀC；1H NMR (300 MHz,
DMSO-d6/TMS)
d
: 5.92 (s, 2H), 6.78 (t, J ¼ 7.8 Hz, 1H), 6.87e6.93 (m,
3.1. Synthesis
2H), 7.25e7.31 (m, 5H), 7.39 (t, J ¼ 7.5 Hz,1H), 7.68 (t, J ¼ 8.4 Hz,1H),
7.83 (d, J ¼ 8.4 Hz, 1H), 8.53 (d, J ¼ 7.8 Hz, 1H), 8.84 (s, 1H), 9.06 (d,
J ¼ 0.9 Hz, 1H), 9.20 (d, J ¼ 0.6 Hz, 1H), 9.23 (s, 1H), 11.64 (s, 1H),
The route used for the preparation of b-carbolines 4 was carried
out as outlined in Fig. 2. Initially, the synthesis of the compounds 2
was realized in three steps starting from the commercially available
12.52 (s, 1H). 13C NMR (75 MHz, DMSO-d6/TMS)
d: 46.19, 110.88,
115.18, 117.29, 118.70, 119.10, 120.39, 120.66, 120.85, 122.64, 126.88,
127.59, 128.25, 128.73, 129.08, 131.48, 137.07, 137.63, 138.96, 141.35,
145.59, 146.15, 149.75, 161.10. ESI-MS m/z: 437.2 (M þ H)þ. Anal.
calcd for C26H20N4O3: C 71.55, H 4.62, N 12.84; found: C 71.59, H
4.78, N 12.67.
L
-tryptophan according to the procedure described in the literature.
Subsequently, the compounds 2 were converted into -carboline-3-
b
carbohydrazides 3 by the treatment with 80% hydrazine hydrate in
ethanol under reflux. Finally, refluxing of 3 with the properly
substituted aryl aldehydes in anhydrous ethanol gave compounds 4.

Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
515
Table 1
Crystal data and structure refinement.
Compound
4a
4d
4e
4f
Empirical formula
Formula weight
Temperature (K)
Crystal system,
Space group
Unit cell dimensions
a (nm)
C23H18N4O3
398.41
298(2)
Orthorhombic
Pca21
C30H22N4O2
470.52
298(2)
Monoclinic
P21/c
C55H47N9O7
946.02
298(2)
Triclinic
P1
C29H27N5O4
509.56
298(2)
Triclinic
P1
2.216(2)
0.7772(3)
1.0077(6)
1.0503(9)
b (nm)
c (nm)
0.6115(6)
1.3719(13)
90
90
90
1.859(3), 4
1.423
0.097
1.8421(7)
1.6310(6)
90
93.822(7)
1.0889(6)
2.4343(13)
87.857(9)
85.330(9)
64.592(9)
2.405(2), 2
1.306
0.089
1.1508(10)
1.2283(11)
64.797(14)
81.612(13)
76.373(14)
1.304(2), 2
1.298
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
90
Volume (nm3), Z
2.3299(15), 4
1.341
0.086
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F (0 0 0)
)
0.089
536
832
984
992
Crystal size (mm)
q
0.23 ꢂ 0.12 ꢂ 0.08
1.84 to 25.05
ꢁ26 ꢃ h ꢃ 25
ꢁ7 ꢃ k ꢃ 7
ꢁ16 ꢃ l ꢃ 13
8936/2996 [Rint ¼ 0.0842]
0.9923 and 0.9780
2996/0/273
1.005
R1 ¼ 0.0632
wR2 ¼ 0.1328
R1 ¼ 0.1172
wR2 ¼ 0.1609
0.0047(13)
220 and 213
879,674
0.21 ꢂ 0.16 ꢂ 0.12
1.67 to 25.05
ꢁ9 ꢃ h ꢃ 9
ꢁ21 ꢃ k ꢃ 18
ꢁ17 ꢃ l ꢃ 19
11,933/4115 [Rint ¼ 0.0262]
0.9897 and 0.9821
4115/0/327
1.026
R1 ¼ 0.0390
wR2 ¼ 0.0927
R1 ¼ 0.0570
wR2 ¼ 0.1038
0.0053(7)
0.23 ꢂ 0.18 ꢂ 0.12
1.68 to 25.05
ꢁ11 ꢃ h ꢃ 11
ꢁ12 ꢃ k ꢃ 12
ꢁ28 ꢃ l ꢃ 20
12,577/8412 [Rint ¼ 0.0228]
0.9894 and 0.9799
8412/0/645
1.025
R1 ¼ 0.0510
wR2 ¼ 0.1206
R1 ¼ 0.1030
wR2 ¼ 0.1502
0.0039(7)
0.21 ꢂ 0.16 ꢂ 0.11
1.83 to 25.05
ꢁ12 ꢃ h ꢃ 12
ꢁ13 ꢃ k ꢃ 9
ꢁ14 ꢃ l ꢃ 14
range for data collection (ꢀ)
Limiting indices
Reflections collected/unique
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
6770/4567 [Rint ¼ 0.0148]
0.9903 and 0.9816
4567/0/345
1.034
R1 ¼ 0.0447
[I > 2sigma(I)]
R indices (all data)
wR2 ¼ 0.1154
R1 ¼ 0.0600
wR2 ¼ 0.1296
Extinction coefficient
Largest diff. peak and hole (e.nmꢁ3
CCDC
)
219 and 190
879,675
289 and 219
879,676
221 and 168
879,677
The chemical structures of all the synthesized novel compounds
were confirmed by 1H NMR, 13C NMR, ESI-MS and elemental
analyses data. Obviously, the 1H NMR spectra of all compounds 4
O2eH2.N4 ¼ 145ꢀ) hydrogen bond is observed in the molecular
structure of 4a. Meanwhile, the molecules are linked together by
intermolecular NeH.O (N1eH1.O2i: N1eH1
¼
0.086 nm,
showed
¼ 8.73e9.87 ppm for the imino proton (CH ¼ N). Additionally,
compounds 4ae4c gave characteristic singlet at
a
well distinguishable intensive singlet signal at
H1.O2 ¼ 0.2264 nm, N1.O2 ¼ 0.3061 nm, N1eH1.O2 ¼ 154ꢀ,
symmetry code: (i) ꢁx þ 1, ꢁy, z þ 1/2) hydrogen bonds into
a one dimensional structure extending along the c axis (Fig. 5),
which are cross-linked into a two-dimensional framework by
intermolecular OeH.N, OeH.O and NeH.O hydrogen bonds
d
a
d
¼ 12.04e12.09 ppm in DMSO, which was assigned to H-9 of the
b-
carboline nucleus. Nevertheless, in the cases of 4de4g, such
a characteristic singlet for H-9 was absent in the 1H NMR spectra,
(O3eH6.N2ii: O3eH6
O3.N2 0.3122 nm, O3eH6.N2
O3eH7 ¼ 0.085 nm, H7.O1 ¼ 0.2047 nm, O3.O1 ¼ 0.2850 nm,
¼
0.085 nm, H6.N2
¼
0.2533 nm,
owing to the N9-benzylation of the
b-carboline nucleus.
¼
¼
127ꢀ; O3eH7.O1:
O3eH7.O1
¼
157ꢀ; N3eH3.O3iii: N3eH3
¼
0.086 nm,
3.2. Crystal structure
H3.O3 ¼ 0.2188 nm, N3.O3 ¼ 0.3015 nm, N3eH3.O3 ¼ 161ꢀ;
X-ray diffraction crystal structure analysis reveals that the four
molecules, 4a, 4d, 4e and 4f, are remarkably similar. All four
molecules adopt a trans configuration about the central C]N
double bonds and exist in the ketoeimine tautomeric form.
Moreover, in each of compounds, the central hydrazone component
is also effectively planar with an all-trans extended conformation,
as exemplified by the relevant torsion angles, and the trans
configuration of the carboxyamido carbonyl oxygen atom and the
nitrogen atom of the pyridine ring can be appreciated. This is in
marked contrast to the side chain conformation observed in methyl
b
-carboline-3-carboxylate, in which the cis conformation is
observed [29].
Compound 4a crystallizes in the orthorhombic space group
Pca21 and has a very near planar structure with a dihedral angle of
5.2ꢀ between the naphthalene ring and the carboline ring system,
which is essentially planar as expected (Fig. 4). Obviously, the
N4eC13 (0.1288(6) nm) and O1eC12 (0.1224(6) nm) bonds feature
C]N and C]O double bonds.
Fig. 4. (a) The molecular structure of 4a, showing the atom-labeling scheme.
Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as
small spheres of arbitrary radius. Water molecule is omitted for clarity. (b) The side
elevation of 4a. Water molecule and H atoms are omitted for clarity.
A
strong
intramolecular
O2eH2.N4
(O2eH2.N4:
O2eH2 ¼ 0.082 nm, H2.N4 ¼ 0.1782 nm, O2.N4 ¼ 0.2498 nm,

516
Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
Fig. 5. Packing diagram of the cell of 4a, viewed down the crystallographic b axis (a) and down the c axis (b).
symmetry code: (ii) ꢁx þ 1, ꢁy þ 1, z e 1/2; (iii) ꢁx þ 1, ꢁy þ 1,
z þ 1/2). The water molecule plays a significant role in the crystal
packing as it is the acceptor in one hydrogen bond and a donor in
another. As a result, the molecules are further self-assembled to
form a well-ordered herringbone structure (Fig. 5).
plane which is almost perpendicular to the phenyl ring. Further-
more, this is evident from the observed distances of N1eC11
(0.12800(19) nm) and O1eC12 (0.12128(18) nm) which are
consistent with carbonenitrogen and carboneoxygen double
bonds, respectively.
The crystal structure of 4d is given in Fig. 6. The compound
crystallizes in monoclinic P21/c space group. Unlike molecule 4a,
this molecule is clearly not planar due to the N9-benzylation of the
Additionally, a stable six-membered ring can be formed through
intramolecular hydrogen bond (O2eH2.N1: O2eH2 ¼ 0.082 nm,
H2.N1 ¼ 0.1861 nm, O2.N1 ¼ 0.2585 nm, O2eH2.N1 ¼ 147ꢀ).
Meanwhile, the molecules are linked together by weak intermo-
b-carboline nucleus. As can be seen from Fig. 6， the molecule of
the group carboline itself is planar, and makes a dihedral angle of
6.4ꢀ with the naphthalene ring, but forms a dihedral angle of 86.1ꢀ
with the phenyl ring (Fig. 6). Thus, apart from the terminal benzyl
group, the rest of the molecule lies approximately in a common
lecular CeH.O (C6eH6.O1iv: C6eH6
¼
0.093 nm,
H6.O1 ¼ 0.2393 nm, C6.O1 ¼ 0.3313 nm, C6eH6.O1 ¼ 169.8ꢀ;
C7eH7.O2iv: C7eH7
¼
0.093 nm, H7.O2
¼
0.2550 nm,
C7.O2 ¼ 0.3443 nm, C7eH7.O2 ¼ 161.1ꢀ; symmetry code: (iv)
ꢁx þ 1, y þ 1/2, ꢁz e 1/2) hydrogen bonds into a zigzag one-
dimensional chain running along the b-axis (Fig. 7), which are
further assembled to form a layer structure (Fig. 7).
Compound 4e crystallizes in the triclinic space group P1, and
forms crystalline clathrates with DMF in a 2:1 M ratio. In this
molecule, there are two crystallographically independent but
conformationally almost identical molecules in the asymmetric
unit (Fig. 8). Moreover, in each molecule, the carboline moiety
appears to be fully planar. The bond geometries show good
agreement with each other. However, they differ with respect to
torsion angle as well as in the dihedral angles. For example, the
dihedral angle between the carboline ring plane and the benzyl
phenyl ring plane in B is 81.6ꢀ, slightly larger than the value of 75.4ꢀ
found in A, but less than the corresponding value of 86.1ꢀ in 4d.
Likewise, the dihedral angle between the carboline ring and the
hydroxyphenyl ring in B is 10.1ꢀ, obviously larger than the value of
3.7ꢀ found in A.
In the crystal structure, 4e shows an intramolecular hydrogen
bond between the O2 and N4 or O5 and N8 atoms (O2eH2.N4:
O2eH2 ¼ 0.082 nm, H2.N4 ¼ 0.1876 nm, O2.N4 ¼ 0.2598 nm,
O2eH2.N4
H5.N8
¼
146ꢀ; O5eH5.N8: O5eH5
¼
0.082 nm,
0.2687 nm,
¼
0.1969
nm,
O5.N8
¼
O5eH5.N8 ¼ 146ꢀ), forming a six-membered ring, which is
coplanar. Two 4e and a DMF solvent molecule are linked by inter-
molecular
N3eH3A
NeH$$$O
and
nm,
OeH$$$O
H3A.O7
((N3eH3A$$$O7:
0.2107 nm,
151ꢀ; O3eH3$$$O4:
Fig. 6. (a) The molecular structure of 4d, showing the atom-labeling scheme.
Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as
small spheres of arbitrary radius. (b) The side elevation of 4d. H atoms are omitted for
clarity.
¼
0.086
¼
N3.O7
¼
0.2888 nm, N3eH3.O7
¼
O3eH3 ¼ 0.082 nm, H3.O4 ¼ 0.1868 nm, O3.O4 ¼ 0.2685 nm,

Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
517
Fig. 7. (a) The one dimensional structure formed via hydrogen bonds in 4d. (b) A packing diagram for 4d, viewed down the b axis.
O3eH3.O4 ¼ 174ꢀ) hydrogen bonds into a hydrogen-bonded
O2.N4 ¼ 0.2583 nm, O2eH2.N4 ¼ 145ꢀ), forming an S(6) ring
trimer. Further, the trimers are linked by intermolecular
motif. On the other hand, the molecules are linked by pair-wise self
OeH,,,O
(O6eH6,,,O1v:
O6eH6
¼
0.082
nm,
complementary O3dH3A.O1 (O3eH3A,,,O1vi: O3eH3A
¼
H6.O1 ¼ 0.1871 nm, O6.O1 ¼ 0.2675 nm, O6eH6.O1 ¼ 166ꢀ;
symmetry code: (v) x, y þ 1, z) hydrogen bonds into a zigzag one-
dimensional chain along the b-axis (Fig. 9), which are further
extended into a three dimensional supramolecular architecture
through the weak intermolecular CeH.O hydrogen bonds and
0.082 nm, H3A.O1
¼
0.1962 nm, O3.O1
¼
0.2710 nm,
O3eH3A.O1 ¼ 151ꢀ; symmetry code: (vi) ꢁx, ꢁy, ꢁz) hydrogen
bonding interactions into a centrosymmetric dimer, with the
formation of an R22ð20Þ ring motif as shown in Fig. 11. Two DMF
solvent molecules are connected to the dimer on both sides through
intermolecular N3eH3.O4 hydrogen bonds (N3eH3.O4:
N3eH3 ¼ 0.086 nm, H3.O4 ¼ 0.2053 nm, N3.O4 ¼ 0.2867 nm,
N3eH3.O4 ¼ 157ꢀ), thus generating the symmetric hydrogen-
bonded tetramer (Fig. 11). The tetramers are held together by the
pe
p
stacking interactions (Fig. 9).
The compound 4f forms crystalline clathrates with DMF in
a 1:1 M ratio and crystallizes in the triclinic space group P1. Both
the carboline and hydroxyphenyl rings are rotated out of the plane
of the central hydrazone component (Fig. 10), forming dihedral
weak intermolecular CeH.O hydrogen bonds and
pep stacking
angles of 11.4 and 8.7ꢀ with it. Moreover, the planar
b
-carboline
interactions to form an extended layer structure (Fig. 11). These
structural characteristics of compound 4f are different from those of
in 4e, though 4f is an isomer of 4e.
Notably, four compounds showed three different space groups
(orthorhombic space group: Pca21 for 4a; monoclinic space group:
P21/c for 4d; triclinic space groups: P1 for 4e and 4f). Thus, the
introduction of substituents onto carboline-hydrazone unit is
considered to change the crystal structure due to the effect of the
ring system makes a dihedral angle of 4.1ꢀ with the hydrox-
yphenyl ring, but forms a dihedral angle of 78.2ꢀ with the benzyl
phenyl ring. Consequently, the whole compound is not a planar
molecule.
As shown for 4a, 4d and 4e, in this compound there is also an
intramolecular hydrogen bond between the O2 and N4 atoms
(O2eH2,,,N4: O2eH2
¼
0.082 nm, H2.N4
¼
0.1869 nm,

518
Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
Compounds 4a and 4d have similar absorption spectra. Broadly,
there are four distinct absorption bands in the range of
250e530 nm. Typically, the first absorption band in the region
400e480 nm reflects an intramolecular charge transfer (ICT) band
of the entire conjugated molecule; two intense structured bands,
the second and third absorption bands, one covering the range
340e400 nm and the other in the range 300e340 nm, are observed.
There is not much difference between the absorption spectra of 4a
and 4d apart from the nontrivial enhancement of absorption
intensity in the long wavelength region for 4a. This indicates that
the N9-benzylation of the b-carboline nucleus has a slight influence
on the absorption spectra and causes only a slight change in the
spectra.
Absorption spectral features of 4e are extremely similar to those
of 4b. The only difference is a slightly red shift of maximum of
absorption peak for 4e. However, in the case of 4f, the absorption
spectrum is characterized by an intense broad absorption from 250
to 380 nm. Within this broad absorption profile there is evidence of
three main peaks with lmax values of 265, 296 and 324 nm. Besides,
one clear shoulder peak at around 360 nm was also observed in the
range of longer wavelength. Nevertheless, these spectral behaviors
are different from those of 4e, though 4f is an isomer of 4e. The
maximum absorption peak (324 nm) for 4f is blue-shifted by 18 nm
as compared with 4e. Considering such a hypsochromic shift, one
can say that the electronic effect of the 2,3-hydroxyphenyl group is
weaker than that of the 2,4-hydroxyphenyl group.
Additionally, it is worth noting that three compounds, 4c, 4f and
4g, have the very similar spectral shape, owing to their very similar
structure. Of course, the similarity in the absorption spectra of
these compounds suggests that the methylation of 4f almost does
not change the absorption spectrum.
The results above imply that more
p-electrons and more
extended -conjugated system may be involved in 4a and 4d than
p
those in the other samples. This may be related to the greater
electron-donating ability of the end naphthalene unit. As a result,
the red-shift of absorption can possibly occur.
3.4. Emission properties
The photoluminescence properties of these molecules in solu-
tion are first studied. It can be seen from Fig. 13 that all of
compounds, except 4f, in the present investigation evidence two
fluorescence bands, the first one in the range 350e440 nm and the
second one centered at around 500 nm. While the strong emission
peak 497 nm is observed for 4a and 4d, the corresponding emission
peak of 4b and 4e appears around 500 nm, which showed a slight
bathochromic shift. But, for compounds 4c and 4g, such a longer
wavelength emission is very weak and almost unnoticeable. In the
case of 4f, the fluorescence spectrum is obviously different from
those of its analogs (4b, 4c, 4e and 4g) due to the absence of
emission peak at w500 nm.
The results above imply that all compounds are fluorescent in
solution. Compounds 4a, 4b and 4d present green emission of
fluorescence, but the other four compounds have their dominant
emission peaks located at 380 nm, which correspond to the ultra-
violet (UV) emission.
Fig. 8. (a) The molecular structure of 4e, showing the atom-labeling scheme.
Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as
small spheres of arbitrary radius. DMF molecule is omitted for clarity. (b) The side
elevation of 4e. DMF molecule and H atoms are omitted for clarity.
nature and position of the substituents. The formation of ordered
structures from these compounds is expected to have a potentially
large impact on their optoelectronic properties in the solid state.
3.3. Absorption spectra
In most cases, organic fluorophores that fluoresce in solution
suffer from fluorescence quenching, showing little or no fluores-
cence in the solid state. Thus, to gain a deep insight into the solid-
state emission behaviors of these derivatives, the solid-state
photoluminescence was measured. The solid-state photo-
luminescence studies were performed at room temperature, using
a heliumecadmium laser (325 nm) as the excitation source.
Analysis of the solid-state fluorescence properties of the deriv-
atives reveals an unexpected behavior: under the 325 nm laser
UVevis absorption spectra of these molecules in diluted DMF
solutions are given in Fig. 12. As shown in Fig. 12, several absorption
peaks could be observed in the linear absorption spectra of 4 in the
wavelength range from 250 to 530 nm, while almost no linear
absorption was observed beyond 530 nm. Such multi-peak profiles
in the linear absorption spectra indicate that these molecules in the
excited state suffer structure distortions in the
frameworks.
p-conjugated

Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
519
Fig. 9. (a) The one dimensional structure formed via hydrogen bonds in 4e. (b) A packing diagram for 4e, viewed down the c axis.
excitation, all compounds display moderate to intense solid-state
fluorescence (Fig. 14). Of seven chromophores only 4f and 4g
emit yellow light, with the others emitting green light (Fig. 15).
At the same time, in comparison with the data recorded in the
dilute solutions, the dyes exhibit very different emissions when in
the solid state, as shown in Fig. 14. Obviously, only an emission
peak, located in the range of 505e582 nm, could be observed in the
solid-state fluorescence spectra of these molecules. Noticeably, in
the solid-state case we did not observe the UV band, which was
noted for the DMF solution. Moreover, the emission peaks of 4
undergo a red-shift from 4a (505 nm) to 4e (520 nm), 4b (523 nm),
4d (527 nm), 4c (540 nm), and to 4f, 4g (582 nm).

520
Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
Fig. 10. (a) The molecular structure of 4f, showing the atom-labeling scheme.
Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as
small spheres of arbitrary radius. DMF molecule is omitted for clarity. (b) The side
elevation of 4f. DMF molecule and H atoms are omitted for clarity.
Among these dyes, crystal 4a shows a very strong green fluo-
rescence emission peak at 505 nm along with a distinct shoulder at
about 480 nm, and possesses the highest fluorescence intensity in
spite of the shortest peak wavelength of emission relative to the
other compounds. Comparison with 4a, the maximum emission
peak of compound 4d is red-shifted by 22 nme527 nm, and an
extended shoulder on the longer wavelength side of main peak in
4d is clearly evident. This difference may be attributed to both
Fig. 11. (a) View of the hydrogen-bonded tetramer in 4f. (b) A packing diagram for 4f,
viewed down the c axis.
the N9-benzylation of the
b-carboline nucleus and the packing
structure.
mentioned above, the crystal structure analysis results reveal that
the main driving forces in the formation of the extended structures
Except for a slight blue shift below 3 nm, the observed emission
profile of 4e is almost identical to that of 4b. Whereas the
maximum emission peak of 4f is significantly red-shifted by 62 nm
with respect to that of 4e. In addition, the maximum emission peak
of 4c is blue-shifted to 540 nm, when compared to 4f and 4g, but
red-shifted by about 17 nm relative to that of 4b. Thus, by
comparing the emission peaks from 4e and 4f, it appears that the
are intermolecular hydrogen bonding and
interactions.
pe
p
stacking
hydroxy substitution of b-carbolines at different positions leads to
the difference of emission properties.
Besides, a maximum 8-fold increase in fluorescence emission
intensity is observed from 4g, as compared with 4f, implying that
the significant emission enhancement can be attained by the
methylation of the 3-OH group of the dihydroxyphenyl ring in 4f.
Actually, the significant difference of photoluminescence
spectra features between in the solution and in the solid state may
possibly be attributable to the fact that the photoluminescence
spectrum of a luminescent molecule in dilute solution reflects
mainly its single molecular characteristics, while the photo-
luminescence spectrum of the same luminescent molecule in
organic crystal form results from the interaction of large numbers
of molecules. Consequently, solid dyes exhibit red-shifted emis-
sions, relative to these observed in solution, indicating that inter-
chromophore interactions exist in their packing structures. The
presence of the intermolecular interactions has been demonstrated
by X-ray diffraction crystal structure analysis in this work. As
Fig. 12. Absorption spectra of compounds
4 in DMF solution (Concentration:
2.0 ꢂ 10ꢁ5 M for 4c, 4d and 4g; 2.3 ꢂ 10ꢁ5 M for the rest).

Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
521
Fig. 14. Photoluminescence spectra of compounds 4 in the solid state. The inset depicts
the expanded photoluminescence spectra of compounds 4b, 4e and 4f.
Fig. 13. Photoluminescence spectra of compounds 4 in DMF solution (Concentration:
2.0 ꢂ 10ꢁ5 M for 4c, 4d and 4g and 2.3 ꢂ 10ꢁ5 M for the rest; Excitation wavelength:
364 nm for 2a and 2d, 342 nm for 2b and 2e, 322 nm for 4c, 4f and 4g). The inset
depicts the expanded photoluminescence spectra of compounds 4c, 4f and 4g.
Fig. 15. Photographs of 4 in solid state under room light (top row) and under 365 nm UV light (bottom row).
Considering the above findings, it is strongly suggested that the
solid-state luminescent properties are dependent closely on the
molecular arrangements and also on the intermolecular interac-
tions of the fluorophores, and the nature and position of the
substituents play principle roles in modulation of molecular
arrangements in the solid state.
Therefore, it has been concluded that the formation of inter-
molecular interactions between the fluorophores is responsible for
the red-shift of the fluorescence maxima and the remarkable
increase in the solid-state fluorescence for 4c and 4g from DMF to
the solid state. Unfortunately, we could not obtain sufficient sizes of
single crystals for 4c and 4g to carry out the X-ray structural
analysis, however, the relatively strong fluorescence intensity for
the crystals of 4c and 4g demonstrated that the methylation of the
3-OH group in the dihydroxyphenyl ring can effectively prevent the
formation of the dimer through intermolecular hydrogen bonds,
thus explaining solid-state emission enhancement from 4c and 4g.
space group Pca21, while 4d in monoclinic space group P21/c, and
the other two, 4e and 4f, were found to be triclinic, with space
group P1. Our findings clearly show that the b-carbolines that are
fluorescent in solution display solid-state fluorescence as well. By
varying the substituent groups on the carboline unit, the solid-state
emission ranging from 505 to 582 nm can be readily obtained.
Significantly, compound 4g shows a strong yellow emission
(
lmax ¼ 582 nm) with a maximum 8-fold increase in fluorescence
emission intensity as compared with 4f.
The results showed that the nature and position of the substit-
uents have significant influences on the crystal structure and
fluorescence properties. The present study can contribute to the
development of efficient fluorescent solid materials.
5. Supplementary material
The crystallographic data (excluding structure factors) of 4a, 4d,
4e and 4f have been deposited with the Cambridge Crystallo-
graphic Center as supplementary publication no. 879,674, 879,675,
879,676 and 879,677, Y, Z AND T. Copy of this information may be
obtained free of charge via www: http://www.ccdc.cam.ac.uk or
from The Director, CCDC, 12 Union Road, Cambridge CB221EZ, UK
(fax: þ44 1223/336 033; email: deposite@ccdc.cam.ac.uk). Struc-
tural factors are available on request from the authors.
4. Conclusions
In summary, in this work, we have reported the synthesis,
characterization, structure and photoluminescence properties of
a series of organic chromophores based on the
b-carboline moiety.
X-ray analyses revealed that 4a crystallize in the orthorhombic

522
Y.-F. Sun et al. / Dyes and Pigments 95 (2012) 512e522
[14] García-Zubiri IX, Burrows HD, Melo JSS, Monteserín M, Arroyo A, Tapia MJ.
A spectroscopic study of the interaction of the fluorescent -carboline-3-
Acknowledgments
b
carboxylic acid N-methylamide with DNA constituents: nucleobases, nucleo-
sides and nucleotides. J Fluoresc 2008;18:961e72.
[15] Guan H, Liu X, Peng W, Cao R, Ma Y, Chen H, et al. b-Carboline derivatives:
This work is supported by the Nature Science Foundation of
Shandong Province of China (No. ZR2010BM032).
novel photosensitizers that intercalate into DNA to cause direct DNA
damage in photodynamic therapy. Biochem Biophys Res Commun 2006;
342:894e901.
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